The present invention relates to a vapor deposition reactor for depositing a thin layer of material on a substrate. More particularly, the invention relates to improvements in the structure of the xe2x80x9cshowerheadxe2x80x9d that introduces gaseous source material into the vapor deposition reactor.
It is known to form compound semiconductor layers in a vapor deposition reactor through, for example, metal organic chemical vapor deposition (MOCVD). A vapor deposition reactor of this type typically includes a reaction chamber that contains a support for holding a wafer. The support may be rotatable so that the wafer can be rotated during the deposition process. A showerhead generally seals the upper end of the reactor chamber. The showerhead includes a number of gas inlets that facilitate the separate introduction of precursor and carrier gasses into the chamber.
Conventional showerheads generally have complex inlet line configurations. One such example is the rotating disc reactor sold by EMCORE under the name TurboDisc(copyright). With this apparatus, the fitting between the showerhead and the inlet lines requires paired-wrench access, i.e., access for two opposing wrenches, at each inlet line connection location for assembly and maintenance. This greatly complicates design layout, assembly and maintenance of the inlet lines and plumbing.
Another difficulty encountered with conventional rotating disc reactors is depletion and non-uniform injection of the deposition. This is particularly true with larger size reactors capable of handling a larger number of wafers. An article by Thompson et al. entitled xe2x80x9cThe Scaling of CVD Rotating Disk Reactors to Large Sizes and Comparison with Theoryxe2x80x9d, Journal of Electronic Materials, Vol. 25, No. 9, pp. 1487-1494 (1996), the content of which is incorporated herein by reference, describes difficulties in scaling and in achieving uniform injection of the source material into the reaction chamber.
The present invention overcomes and/or minimizes the problems discussed above with respect to the prior art through a specially designed showerhead for a vapor deposition reactor.
According to one aspect of the invention, an apparatus for chemical vapor deposition includes a reaction chamber, a support within the reaction chamber that supports the substrate, and a showerhead that seals one end of the reaction chamber. The showerhead has an outer surface, an inner surface, and a plurality of inlet seal assemblies for permitting the flow of gaseous material through the showerhead into the reaction chamber. A plurality of inlet lines supply gaseous source material to the reaction chamber. The surface seal assemblies each have a seal body that extends through the showerhead, and a collar around the inlet line. The seal body and the collar each have a substantially planar face seal surface. The fittings are connected to the inlet seals such that face seal surface of each collar abuts the face seal surface of one of the seal bodies. The invention may also include clamping means, such as clamping screws, for causing the face seal surfaces to press together, thereby creating the seal between inlet lines and the inlet seal assemblies. Preferably, the face seal surfaces of the seal bodies are all substantially coplanar to each other and parallel to the outer surface of the showerhead.
According to this first aspect of the invention, the showerhead is surface sealing. In other words, the connection of the inlet lines to the inlet assemblies occurs by pressing of the planar seal surfaces together. The connection of these seals requires only a single tool and the seal clamping screws are easily accessed. Such design makes it easier to connect, clean and maintain the input vapor lines and enhances the flexibility of the inlet line layout. Moreover, it allows the seals between the inlet lines and the showerhead to be formed substantially flush with the upper surface of the showerhead.
According to a second aspect of the invention, an apparatus for chemical vapor deposition includes a reaction chamber, a support disposed within the reaction chamber that supports the substrate, and a showerhead that seals one end of said reaction chamber. The showerhead has an outer surface, an inner surface, a plurality of inlet seal assemblies extending through said inner and outer surfaces so as to permit the flow of gaseous material through the showerhead into the reaction chamber, and a gas dispersion assembly formed on the inner surface of the showerhead. The gas dispersion assembly defines a plurality of cavities, each of which is positioned to receive gaseous material exiting from one of the inlet seal assemblies. The gas dispersion assembly has at least one flow diverter for diverting the flow of gaseous material out of one of the inlet seal assemblies and into one of the cavities, and at least one diffuser screen for diffusing gaseous material as it passes from the cavities into the reaction chamber.
According to this second aspect of the invention, the gas dispersion assembly preferably includes a number of open webbed plates. These plates support the gas dispersion screen(s) and preferably have integrated into them the gas flow diverters that redirect the gas streams entering the reactor via the inlet seals. The cavities are defined on their sides by the arms of these open webbed plates and on their surfaces by the inner surface of the showerhead and/or by the diffuser screens. The cavities can be spaced radially and/or concentrically so that the flow of gaseous material into the chamber can be selectively controlled. In this way, the present invention facilitates uniform deposition of materials while simplifying part cleaning, assembly and maintenance by reducing the number of parts.
Thus, the invention simplifies/streamlines the achievement of optimal flows for chemical vapor deposition of preferably uniform or uniformly conformed thin films and multi-layer films of desired composition, including porous, dense, amorphous, polycrystalline or crystalline film types or multi-layer mixtures of said film types.